1. Field of Invention
This invention concerns methods for the detection of an irregularity in an object based on an image of the object. One embodiment is related generally to systems and methods for the detection of a defect in a solder element based on an X-ray image of the solder element.
2. Discussion of Related Art
Surface mount technology (“SMT”) is an electronic circuit assembly process in which surface-mount devices, components, or parts, such as resistors, capacitors, integrated circuit packages, and the like, are soldered onto the surface of a printed circuit board (“PCB”). This differs from “leaded” or “through-hole” technology, in which leads of the device are inserted into holes in the PCB.
Among the variety of existing surface-mount packages for integrated circuits (“ICs”) is the Ball Grid Array (“BGA”). While other surface-mount IC packages have pins extending from the sides of the package (e.g., the Dual In-line Package and the Quad Flat Package), BGA packages employ an array of spheres or balls of solder attached to the bottom surface of the package as external electrical interconnects. The solder balls can lie over all or a portion of the bottom surface of the package.
To assemble the BGA package on a printed circuit board, the BGA solder balls are first placed on corresponding solder pads on the PCB surface, such as by use of a pick-and-place machine. The PCB is then placed in a reflow oven, in which the solder balls are caused to melt. The solder balls then cool and solidify, soldering the BGA package to the PCB.
A common defect in BGA solder balls is the presence of bubbles of gas, known as voids, in the solder. Depending on the quantity of voids in the solder ball, their size relative to the size of the solder ball, and their location in the solder ball, voids can affect the quality and/or reliability of the resulting solder joints. In order to ensure the quality of the solder joints, therefore, it is necessary to inspect solder balls to detect occurrences of voids and measure their characteristics. Characteristics of interest may include position, diameter, depth, area, volume, and the like.
Due to the fact that they are hidden below the surface of the solder ball, voids cannot be detected by visual or optical inspection. For this reason, X-ray imaging may be used to inspect solder balls for voids.